Used in bioconjugation to link proteins, peptides, or nanoparticles with high specificity. The maleimide group reacts efficiently with thiol groups (-SH) on cysteine residues or thiolated molecules, forming stable thioether bonds. The NHS ester end reacts with primary amines (-NH₂) on biomolecules, enabling crosslinking or labeling. Commonly applied in drug delivery systems, antibody-drug conjugates (ADCs), and surface functionalization of materials for biosensors or diagnostic devices. Its PEG spacer improves solubility, reduces aggregation, and enhances biocompatibility in biological environments.